A fixed type constant velocity universal joint is an example of a constant velocity universal joint used as means for transmitting torque from the engine of an automobile to the wheels at constant velocity. The fixed type constant velocity universal joint connects two shafts on the driving side and the driven side and is provided with a structure allowing constant-velocity transmission of rotational torque even when the two shafts form an operating angle. Generally, as an example of the widely-known fixed type constant velocity universal joint described above, there may be given one adopting a birfield type (BJ) or an undercut free type (UJ).
For example, the fixed type constant velocity universal joint of the BJ type includes an outer joint member having opened one end and an inner spherical surface in which multiple track grooves are equiangularly formed in an axial direction, an inner joint member having an outer spherical surface in which multiple track grooves paired with the track grooves of the outer joint member are equiangularly formed in the axial direction, multiple balls interposed between the track grooves of the outer joint member and the track grooves of the inner joint member, for transmitting torque, and a cage interposed between the inner spherical surface of the outer joint member and the outer spherical surface of the inner joint member, for retaining the balls.
The multiple balls are equiangularly arranged while being accommodated in pockets formed in the cage. Further, internal components including those inner joint member, balls, and cage are accommodated inside the outer joint member. The inner joint member has a shape in which the outer spherical surface thereof has multiple protruding portions formed between the track grooves.
When a constant velocity universal joint of this type is used, for example, for an automotive drive shaft, there is generally employed the structure in which the outer joint member is connected to a driven shaft, and a drive shaft extending from a plunging type constant velocity universal joint mounted to a differential on the vehicle body side is connected to the inner joint member through spline fit-engagement. In this constant velocity universal joint, when an operating angle is formed between the outer joint member and the inner joint member, the balls accommodated in the cage are always maintained within the bisector plane of any operating angle, thereby securing the constant velocity property of the joint.
In the fixed type constant velocity universal joint, generally, the inner joint member is assembled to the cage by the following procedures. First, the inner joint member is arranged relatively to the cage in the direction of being rotated by 90° with respect to the axial direction of the cage. Then, in a state of fitting one of the protruding portions positioned between the track grooves of the inner joint member into one of the pockets of the cage, the inner joint member is inserted into the cage. The center of the inner joint member and the center of the cage are caused to correspond to each other, and then the inner joint member is rotated by 90° with respect to the axial direction of the cage. In this manner, the axial line of the cage is caused to correspond to the axial line of the inner joint member, whereby arrangement in a regular posture is achieved (refer to Patent Documents 1 and 2, for example).    Patent Document 1: DE 19514868 C1    Patent Document 2: JP 3678026 B